1. Technical Field
The present disclosure relates generally to the field of sucker rods used in conjunction with rod pumps, and more specifically to methods of assembling sucker rod sections and end fittings into completed sucker rods.
2. Background Art
Fiberglass reinforced plastic (FRP) sucker rods and present manufacturing methods are discussed in various public resources, such as U.S. Pat. No. 7,730,938, to Rutledge, Sr. It is assumed the reader is familiar with FRP sucker rods and their use. As will be noted by reviewing the '938 patent, the known manufacturing process involves many steps. Manufacture of the FRP rod sections that make up the final, complete FRP sucker rod relies on a very expensive pultrusion machine and labor-intensive process. It is an object of the present disclosure to perform only certain assembly steps of a completed FRP sucker rod at or near a point of use, such as at or near a producing hydrocarbon basin, thus reducing the need to purchase and operate an expensive rod section pultrusion machine at such points of use, or to transport completed FRP sucker rods long distances to such points of use, with attendant worries of damage to the rods prior to use.
In addition to the above-mentioned problems attendant to the remote manufacture of FRP sucker rods (both jointed and continuous), the present inventor has noted that the known methods of attaching metallic end fittings to abraded fiberglass rod section ends was in need of improvement. In particular, almost no disclosure has been made of particular abrading materials or methods, or of adhesives used in attaching the end fittings to the abraded ends of the FRP rod sections. The '938 patent provides no teaching or details on these issues.
An additional problem faced by the FRP sucker rod assembler, and so far as can be seen in the patent literature, an underappreciated fact, is that the FRP rods stretch during assembly. In one known assembly process, according to the '938 patent, after the adhesive is applied to the end fitting and the end fitting applied to rod end, the end fitting area is heated to cure the adhesive, and then cooled or allowed to cool. As explained in the '938 patent, the cooled rods are then “pull tested” (pulled longitudinally) to set the mechanical wedge bond between the cured adhesive and the end fitting. According to the '938 patent, the pull test both creates and checks the integrity of the mechanical bond between the rod body and the end fitting. What is not discussed is how the pull test is performed (by a hand crank mechanism), or that the rod itself undergoes stretching during the pull test, the degree of stretch depending on the tension force applied, the type of FRP material, diameter of the rod, and so on. In some instances, the present inventor is aware that a nominal 37 foot (11.3 m) length rod may be stretched up to 11 inches (28 cm) or more. Monitoring and measurement of rod stretch is not currently practiced during pull testing, as far as is known, because the hand crank method and apparatus is not set up to measure this. Although the stretch could be measured by hand, it would be beneficial to know the actual rod stretch measurement precisely, since an FRP rod that stretches even a little too much or too little will be compounded over the length of the connected rods down hole. FRP rods that stretch too much may be an indication that they do not have enough longitudinal glass fiber roving, and therefore may not endure many pumping cycles during use; on the other hand, FRP rods that stretch too little may have too much glass fiber roving, and therefore may be too rigid for many down hole applications, or may not be suitable for winding onto to spools.
The industry has long lived with the above-mentioned problems and has accepted them as facts of the business. There is thus a long-felt but as yet unmet need in the art of assembling FRP sucker rods for methods and systems alleviating these problems. Note that while the '938 patent mentions that end fittings may be attached to a sucker rod at a field location, and that several “conventional” steps can be performed, such as “additional quality control checks or inspections”, there is no description of or directions given how pull testing and stretch measurement would be accomplished at a field location.